Method and apparatus for enhanced CMP using metals having reductive properties

ABSTRACT

Dishing in chemical mechanical polishing (CMP) is reduced by introducing a material that balances electrochemical forces. In a first embodiment of the invention, a polishing pad having copper material in grooves on the polishing pad surface is used in the polishing process to reduce dishing. In a second embodiment of the invention, the polishing pad has perforations with copper fillings. In a third embodiment of the invention, a copper retaining ring on the polishing head introduces copper material to the CMP process to reduce dishing. In a fourth embodiment of the invention, a conditioning plate of copper is used in the polishing apparatus. In a fifth embodiment of the invention, additional copper features are placed on the substrate to be polished. The polishing of the additional features introduces copper steadily through the polishing process. In a sixth embodiment of the invention, copper compounds are added to the polish slurry.

RELATED APPLICATIONS

This application is related to co-pending U.S. patent application Ser.No. 09/910,425 (AMAT/3836.P1), filed on Jul. 20, 2001, and U.S. patentapplication Ser. No. 09/563,628, (AMAT/3836.P1) filed on May 2, 2000.

FIELD OF THE INVENTION

This invention relates generally to planarization of substrates and moreparticularly to chemical mechanical polish of metal substrates.

BACKGROUND OF THE INVENTION

Integrated circuits are typically formed on substrates, particularlysilicon wafers, by the sequential deposition of conductive,semiconductive or insulative layers. After a layer is deposited, thelayer is etched to create circuitry features. As a series of layers aresequentially deposited and etched, the outer or uppermost surface of thesubstrate, i.e., the exposed surface of the substrate, becomesincreasingly non-planar. This non-planar outer surface presents aproblem for the integrated circuit manufacturer. Therefore, there is aneed to periodically planarize the substrate surface to provide arelatively flat surface. In some fabrication processes, planarization ofthe outer layer should not expose underlying layers.

Chemical mechanical polishing (CMP) is one method of planarization. Thisplanarization method typically requires that the substrate be mounted ona carrier or polishing head. The exposed surface of the substrate isplaced against a polishing pad. The polishing pad may be either a“standard” pad or a fixed-abrasive pad. A fixed-abrasive pad hasabrasive particles held in a containment media, whereas a standard padhas a durable surface, without embedded abrasive particles. The carrierhead provides a controllable load, i.e., pressure, on the substrate topush it against the polishing pad. A polishing slurry, including atleast one chemically-reactive agent, and abrasive particles if astandard pad is used, is supplied to the surface of the polishing pad.

An effective CMP process not only provides a high polishing rate, butalso provides a substrate surface which is finished and flat. Thepolishing rate, finish and flatness are determined by the pad and slurrycombination, the relative speed between the substrate and pad, and theforce pressing the substrate against the pad.

In applying conventional planarization techniques, such as CMP, it isextremely difficult to achieve a high degree of surface planarity. Themetal features on the substrate are typically formed in an interlayerdielectric, such as silicon oxide layer, by a damascene techniquewherein trenches are initially formed. A barrier layer, such as atantalum-containing layer e.g. Ta, TaN, or alternatively titanium (Ti orTiN), is then deposited lining the trenches and on the upper surface ofthe silicon oxide interlayer dielectric. Copper or a copper alloy isthen deposited, as by electroplating, electroless plating, physicalvapor deposition (PVD) at a temperature of about 50° C. to about 150° C.or chemical vapor deposition (CVD) at a temperature under about 200° C.,typically at a thickness of about 8000 Å to about 18,000 Å. Thedeposited copper is chemically oxidized and then removed using CMP tocreate features on the metal substrate.

In planarizing the wafer surface after copper metallization using CMP,undesirable erosion and dishing typically occur, decreasing the degreeof surface planarity and challenging the depth of focus limitations ofconventional photolithographic techniques, particular with respect toachieving submicron dimensions, such as about 0.25 micron. In addition,dishing reduces the size of circuit lines thereby increasingresistivity. Erosion is defined as the height differential between theoxide in the open field and the height of the oxide within the circuitarray. Dishing is defined as a difference in height between the oxideand Cu in a feature (i.e. in a line or pad).

Dishing is caused, in general, by differences in hardness and chemicalinteraction across a surface. The mechanical and chemical interactionsbetween the polishing pad and slurry and copper are different from themechanical and chemical interactions between the polishing pad andslurry and oxide.

One of the causes of increased dishing arises from the difference inelectrochemical potential between copper and barrier layer material. Asthe copper removal process approaches the copper/barrier interface, thesubstrate surface has both copper areas and barrier areas. Anelectrochemical effect takes place at the copper/barrier interfacebecause of the electrochemical potential differential. The effect causesenhanced removal of copper in surface features and therefore causeshigher dishing.

A second cause of increased dishing is the chemical loading effect. Asthe amount of copper is cleared from the surface, the ratio of polishingchemical in the slurry to copper on the substrate increases. This changein the chemical equilibrium of the CMP process in turn, enhances copperremoval at surface features on the substrate.

It remains desirable to have a process of planarization where dishing isdecreased.

It is an advantage of the present invention to provide a method andapparatus for substrate planarization producing a good quality substratesurface.

SUMMARY OF THE INVENTION

The problems of reducing dishing while achieving planarized processedsubstrates are solved by the present invention of a polish pad embeddedwith metal material having reductive properties for chemical mechanicalpolish.

Dishing in chemical mechanical polishing (CMP) is reduced by introducinga material that balances electrochemical forces. In a first embodimentof the invention, a polishing pad having copper material in grooves onthe polishing pad surface is used in the polishing process to reducedishing. In a second embodiment of the invention, the polishing pad hasperforations with copper fillings. In a third embodiment of theinvention, a copper retaining ring on the polishing head introducescopper material to the CMP process to reduce dishing. In a fourthembodiment of the invention, a conditioning plate of copper is used inthe polishing apparatus. In a fifth embodiment of the invention,additional copper features are placed on the substrate to be polished.The polishing of the additional features introduces copper steadilythrough the polishing process. In a sixth embodiment of the invention,copper compounds are added to the polish slurry.

The present invention together with the above and other advantages maybest be understood from the following detailed description of theembodiments of the invention illustrated in the drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a substrate with a plurality oflayers;

FIG. 2 is a pictorial exploded view of a chemical mechanical polishingapparatus incorporating aspects of the present invention;

FIG. 3 is a top view of a polishing pad having copper-filled groovesaccording to the principles of the invention;

FIG. 4 is a side cross-sectional view of a first assembly of thepolishing pad of FIG. 3;

FIG. 5 is a side cross-sectional view of a second assembly of thepolishing pad of FIG. 3;

FIG. 6 is a top view of a polishing pad having perforations according toprinciples of the invention;

FIG. 7 is a side cross-sectional view of a first assembly of thepolishing pad of FIG. 6;

FIG. 8 is a side cross-sectional view of a second assembly of thepolishing pad of FIG. 6; and

FIG. 9 is a top view of a wafer having dummy features of a metal havingreductive properties according to principles of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a cross-sectional view of a conductive substrate 10 havingdeposited layers such as those layers formed during the manufacture ofsemiconductors. The figure is not to scale. An interlayer dielectric 20,e.g. silicon oxide, is formed overlying a metal layer 15. A plurality ofindentations, also referred to as openings 25, are formed in adesignated area at the left of the interlayer dielectric 20 in which anarray of conductive lines are to be formed bordering an open field shownon the right of the interlayer dielectric 20. A barrier layer 30, e.g.tantalum, tantalum nitride, titanium or titanium nitride, is depositedon the layer of interlayer dielectric 20, the barrier layer 30 alsolining the plurality of openings 25. A conductive layer 35, e.g. copper,is then deposited over the barrier layer 30. Successive process stepsrequire that portions of the conductive layer be removed. Planarizationand selective removal of the conductive layer are accomplished in apolishing step.

FIG. 2 shows a chemical mechanical polishing apparatus 100 having aplurality of polishing stations 105, 110, 115. The polishing apparatusincludes a lower machine base 120 with a table top 125 mounted thereonhaving the plurality of polishing stations 105, 110, 115. Each polishingstation 105, 110, 115 includes a rotatable platen 130 on which is placeda polishing pad 135, and it further includes an associated padconditioner apparatus 140, 145, 150, each with a rotatable arm 155holding a conditioner head 160 and an associated washing basin 165 forthe conditioner head 155. Each polishing station 105, 110, 115 furtherincludes a slurry arm 142, 148, 152 for delivering polishing slurry.

A rotatable multi-head carousel 170 includes four wafer head systems175, 180, 185, 190 which receive and hold wafers and polish the wafersby pressing them against respective polishing pads 135 held on theplatens 130 at the respective polishing stations 105, 110, 115. Eachwafer head system 175, 180, 185, 190 has a retaining ring 176, 181, 186,191 for retaining the wafer during polish. The carousel 170 is supportedon a center post 195 and is rotated thereon about a carousel axis 200 bya motor assembly located within the base 120.

The four identical wafer head systems 175, 180, 185, 190 are mounted ona carousel support plate 205 at equal angular intervals about thecarousel axis 200. The center post 195 centrally supports the carouselsupport plate 205 and allows the carousel motor to rotate the carouselsupport plate 205, the wafer head systems 175, 180, 185, 190, and thewafers attached thereto about the carousel axis 200. Each wafer headsystem 175, 180, 185, 190 includes a wafer head 210 that is rotatedabout its own axis by a head-rotation motor 215 connected to it by ashaft. The heads 210 can rotate independently as driven by theirdedicated head-rotation motors 215, and can further independentlyoscillate radially in slots 220 formed in the carousel support plate205. Raising or lowering wafers attached to the bottom of the waferheads 210 is performed within the wafer head systems 175, 180, 185.

During the actual polishing, the wafer heads 210 of three of the waferhead systems, e.g., 175, 180, 185, are positioned at and aboverespective polishing stations 105, 110, 115, each having anindependently rotatable platen 130 supporting a polishing pad 135 whosesurface is wetted with an abrasive slurry which acts as the media forpolishing the wafer. During polishing, the wafer head systems 175, 180,185 independently oscillate along respective radii of the carousel 170so that the associated wafer heads 210 move along a diameter of arespective polishing pad 135. In a typical process, the sweep axis of awafer heads 210 is aligned to the center of the polishing pad 135.

In use, the wafer head 210, for example, that of the fourth wafer headsystem 190, is initially positioned above the wafer transfer station225. When the carousel 170 is rotated, it positions different wafer headsystems 175, 180, 185, 190 over the polishing stations 105, 110, 115 andthe transfer station 225. The carousel 170 allows each wafer head system175, 180, 185, 190 to be sequentially located first over the transferstation 225, then over one or more of the polishing stations 105, 110,115, and then back to the transfer station 225.

Each polishing pad 135 can be continuously or periodically conditionedby one of the pad conditioner apparatus 140, 145, 150, each having anindependently rotating conditioner head 160 attached to the conditionerarm 155. An abrasive conditioning plate 162 or a similar conditioningsurface is included at the bottom of the conditioner head 160. The arm155 sweeps the conditioner head 160 across the associated polishing pad135 in an oscillatory motion generally between the center of thepolishing pad 135 and its perimeter. The conditioner head 160 is pressedagainst the pad 135 to abrade and condition the pad so that itthereafter effectively polishes any wafer pressed against it while it isrotating.

FIG. 3 is a top view of a surface 250 of a polishing pad 245 havingembedded copper of a first embodiment of the present invention. Thepolishing pad may be either a “standard” pad or a fixed-abrasive pad. Afixed-abrasive pad has abrasive particles held in a containment media,whereas a standard pad has a durable surface, without embedded abrasiveparticles. The polishing pad surface 250 has a series of concentricgrooves 255. The grooves 255 are for example, 0.025″ wide with a 0.25″pitch. In alternative embodiments of the invention grooves may beapproximately 0.020″-approximately 0.100″ in width. These dimensions aremerely exemplary. Other widths and pitches may be used within the scopeof the invention. Each groove 255 contains copper material 260. Duringthe polishing process, the copper in the grooves 255 in the polishingpad 135 acts to maintain the electrochemical equilibrium over the courseof the CMP process, thereby decreasing the amount of dishing that wouldotherwise take place.

FIG. 4 shows a side cross-sectional view of a first assembly of thepolishing pad 245 of FIG. 3. In this assembly, grooves 255 are formed inthe polishing pad first. Copper tape or wire 260 is then placed in eachgroove 255. In a preferred embodiment, the copper 260 lies below thesurface 250 of the polishing pad, however for electrochemical purposes,the copper could fill the groove to the surface 250 of the polishing pad245 with equal effect. Alternate ways of putting copper into the grooves255 include electroless plating and chemical vapor deposition (CVD).

FIG. 5 shows a side cross-sectional view of a second assembly of thepolishing pad of FIG. 3. A layer of copper foil 280 is placed on a base285. The polishing pad 245 with grooves 255 is then formed on top of thecopper foil layer 280. A first method of forming the second assembly ofthe polishing pad 245 is to place a polishing pad layer on top of thecopper foil layer 280. Grooves 255 are then cut into the polishing paddeeply enough to expose the copper foil layer 280. A second method offorming the second assembly is to cut the grooves in the polishing padlayer an then fixing the polishing pad to the copper foil layer. This ismore readily accomplished by cutting grooves that are not completecircles leaving polishing pad spacers holding the polishing padtogether.

FIG. 6 shows a top view of a second embodiment of the present inventionof a polishing pad 300 having embedded copper. The polishing pad surface305 has a plurality of perforations 310. The perforations are holes thatextend from the surface of the pad some distance into the pad. Thedensity of perforations 310 in a preferred embodiment of the inventionis approximately 10%-20%, however a density anywhere in the range of 5%to 50% falls within the scope of the present invention. In a preferredembodiment, each perforation (or hole) is for example 0.050″ indiameter. The perforations may be in the range of approximately0.010″-approximately 0.150″ in diameter within the scope of theinvention. Each perforation contains copper material. During thepolishing process, the copper in the perforations acts to maintain theelectrochemical equilibrium, thereby decreasing the amount of dishingthat would otherwise take place.

FIG. 7 shows a side cross-sectional view of a first assembly of thepolishing pad 300 of FIG. 6. In this assembly, the perforations, or“holes” 310, are formed in the polishing pad first. The holes 310 arethen filled with copper material 320. The holes 310 can be formed bydrilling or chemical etching. The copper fillings may be introduced byCVD or electroless plating, other mechanical means.

FIG. 8 shows a side cross-sectional view of a second assembly of thepolishing pad 300 of FIG. 6. In this assembly, a layer of copper foil350 is placed on a base 355. The polishing pad 300 with perforatons 310is then formed on top of the copper foil layer 350. A first method offorming the second assembly of the polishing pad 300 is to fasten anunperforated polishing pad layer on top of the copper foil layer 350.Holes 310 are then cut into the polishing pad deeply enough to exposethe copper foil layer 350.

In a third embodiment of the invention, retaining rings 176, 181, 186(shown in FIG. 2) of copper are used both alone and in combination withcopper embedded in.the polishing pad.

In a fourth embodiment of the invention, a conditioning plate 162 (shownin FIG. 2) of copper is used in the polishing pad conditioner apparatus140, 145, 150. The copper conditioning plate 162 leaves an amount ofcopper on the pad after conditioning thus reducing the polishingchemical to copper imbalance.

FIG. 9 shows a fifth embodiment of the invention in which additionalareas of copper (also referred to as dummy features) are included in themetal substrate to be polished. FIG. 9 shows a wafer 370 having aplurality of components 375. Each component 375 is surrounded by a bandof copper 380. The additional copper from these areas maintains theelectrochemical equilibrium during the polishing process. Theconfiguration of dummy features shown in FIG. 9 is merely exemplary.Many other possible configurations of dummy features on a substrate areincluded within the scope of the invention.

In a sixth embodiment of the invention, copper compounds are added tothe slurry 138 (shown in FIG. 2) in order to maintain electrochemicalequilibrium. The copper compounds are typically copper sulfate or someother copper salt. The copper compounds make up, for example, <1% of theslurry 138 by weight.

In further alternative embodiments of the invention, other metals, suchas zinc, may be used instead of copper. Any metal that lowers reductivepotential of the polishing process may be used instead of copper. Thesizes and spacings of grooves and perforations provided herein arepresented as examples. A wide range of dimensions could be used withinthe scope of the present invention. The above-described process may beused to planarize any type of patterned metal wafer.

It is to be understood that the above-described embodiments are simplyillustrative of the principles of the invention. Various and othermodifications and changes may be made by those skilled in the art whichwill embody the principles of the invention and fall within the spiritand scope thereof.

What is claimed is:
 1. A polishing pad for chemical-mechanical polishinga substrate, comprising: a polishing surface; a plurality of concentricgrooves formed in said polishing surface; and metal material embedded inat least one of said plurality of concentric grooves, said metalmaterial having reductive properties, whereby said embedded metal insaid polishing pad reduces dishing in chemical-mechanical polishing thesubstrate.
 2. The polishing pad of claim 1, wherein said metal materialis copper.
 3. The polishing pad of claim 1, wherein said metal materialis zinc.
 4. The polishing pad of claim 1, wherein each said concentricgroove is approximately 0.020″ to approximately 0.100″ wide.
 5. Thepolishing pad of claim 1, wherein said metal material is metal tape. 6.The polishing pad of claim 1, wherein said metal material is metal wire.7. A polishing pad for chemical-mechanical polishing a substrate,comprising: a base layer; a metal foil layer attached to said baselayer; and a polishing pad layer attached to said metal foil layer, saidpolishing pad layer having a plurality of grooves, said grooves cutthrough said polishing pad layer exposing portions of said metal foillayer, whereby said exposed metal foil in said polishing pad reducesdishing in chemical-mechanical polishing the substrate.
 8. A polishingpad for chemical-mechanical polishing a substrate, comprising: apolishing surface; a plurality of holes formed in said polishingsurface; and, metal material embedded in a plurality of said holes, saidmetal material having reductive properties, whereby said embedded metalin said polishing pad reduces dishing in chemical-mechanical polishingthe substrate.
 9. The polishing pad of claim 8, wherein said metalmaterial is copper.
 10. The polishing pad of claim 8, wherein said metalmaterial is zinc.
 11. The polishing pad of claim 8, wherein saidplurality of holes cover between 5% to 50% of the area of said polishingsurface.
 12. The polishing pad of claim 8, wherein each said hole isbetween approximately 0.010″ to approximately 0.100″ wide.
 13. Apolishing pad for chemical-mechanical polishing a substrate, comprising:a base layer; a metal foil layer attached to said base layer; and apolishing pad layer attached to said metal foil layer, said polishingpad layer having a plurality of holes, said holes cut through saidpolishing pad layer exposing portions of said metal foil layer, wherebysaid exposed metal foil in said polishing pad reduces dishing inchemical-mechanical polishing the substrate.
 14. A polishing apparatus,comprising: a polishing head having a retaining ring for retaining asubstrate, said retaining ring formed from a metal having reductiveproperties; and a polishing pad for polishing said substrate, wherebysaid retaining ring having reductive properties reduces dishing inchemical-mechanical polishing.
 15. The polishing apparatus of claim 14,wherein said polishing pad further comprises a polishing surface havingembedded metal, said embedded metal having reductive properties.
 16. Thepolishing pad of claim 14, wherein said embedded metal is embedded ingrooves in said polishing surface.
 17. The polishing pad of claim 14,wherein said embedded metal is embedded in holes in said polishingsurface.
 18. The polishing pad of claim 14, wherein said embedded metalis copper.
 19. The polishing pad of claim 14, wherein said embeddedmetal is zinc.
 20. A polishing apparatus, comprising: a polishing headfor holding a substrate; a polishing pad for polishing said substrate;and a slurry delivery device for delivering slurry having coppercompounds, wherein said copper compounds have reductive propertiesreducing dishing in chemical-mechanical polishing.
 21. A polishingapparatus, comprising: a polishing head for holding a substrate to bepolished; a polishing pad; and a polishing pad conditioning apparatushaving a conditioning plate of metal having reductive properties,whereby an amount of said metal is deposited on said polishing padduring conditioning thereby electrochemical equilibrium of a polishingprocess is maintained.
 22. A substrate for maintaining electrochemicalequilibrium in a polishing process, comprising: a conductive metal base;a plurality of components formed on a surface of said conductive metalbase; at least one dummy feature made of a metal having reductiveproperties on said surface, said dummy feature to maintainelectrochemical equilibrium in the polishing process.
 23. A polishingpad for chemical-mechanical polishing a substrate, comprising: apolishing surface; a plurality of grooves formed in said polishingsurface; and metal tape embedded in at least one of said plurality ofgrooves, said metal tape having reductive properties, whereby saidembedded metal tape in said polishing pad reduces dishing inchemical-mechanical polishing the substrate.
 24. The polishing pad ofclaim 23, wherein said metal tape is copper or zinc.
 25. The polishingpad of claim 23, wherein said plurality of grooves are concentric. 26.The polishing pad of claim 23, wherein each said groove is approximately0.020″ to approximately 0.100″ wide.
 27. The polishing pad of claim 7,wherein said metal foil is copper or zinc.
 28. The polishing pad ofclaim 7, wherein said plurality of grooves are concentric.
 29. Thepolishing pad of claim 7, wherein each said groove is approximately0.020″ to approximately 0.100″ wide.
 30. The polishing pad of claim 13,wherein said metal material foil is copper or zinc.
 31. The polishingpad of claim 13, wherein said plurality of holes cover between 5% to 50%of the area of said polishing surface.
 32. The polishing pad of claim13, wherein each said hole is between approximately 0.010″ toapproximately 0.100″ wide.